1. Field of the Invention
The invention relates generally to circuit interrupters utilizing closing resistance and more particularly to a high voltage circuit interrupter having a precise repeatable closing mechanism utilized to insert a closing resistance in parallel with the main contacts of the circuit interrupter.
2. Description of the Prior Art
It is known that high voltage surges, depending upon circuit conditions, can occur during the closing of the contacts of a high voltage circuit interrupter. One method of reducing such high switching surges is described in U.S. Pat. No. 3,291,947, where a resistance is inserted into the contacts of the circuit interrupter prior to the time of engagement of the main contacts. U.S. Pat. No. 4,072,836 also discloses the use of a resistor inserted into the circuit during the closing operation of a high voltage circuit interrupter.
When interrupting very high voltages, for example, 500 kV, it is not uncommon to utilize two or more individual interrupting heads serially connected to provide the necessary interrupting capacity. This use of multiple interrupting heads can cause coordination problems, particularly with respect to closing on an energized transmission line. This is particularly critical for the insertion of the resistors into the circuit. For correct operation of the resistor insertion scheme, it is essential that the impedance contacts within all the interrupting units close a very short time, for example, 10 milliseconds, before the closing of the main circuit breaker interrupter contacts. During the opening operation of the circuit breaker, however, such closing resistances are not inserted into the circuit, and have no function whatsoever as set forth in U.S. Pat. No. 3,291,947. It is therefore necessary that the impedance contacts open within a few milliseconds after the interrupter contacts are closed. Accordingly, it would be desirable to have a closing resistor insertion mechanism that is characterized by precise repeatability and that is able with a common movement effecting means to close the impedance resistor contacts shortly before the closing of the main circuit breaker interrupter contacts, for example, 10 milliseconds before, and to open them a few milliseconds after the main interrupter contacts are closed.
Some mechanisms for the closing resistor insertion depend upon springs or other variable devices whose characteristics may change after multiple operations. Accordingly, it would also be desirable if the resistor insertion timing mechanism had a rigid mechanical arrangement for at least the insertion operation since this is the operation that must be controlled precisely.